1. Field of the Invention
The present invention relates to an electric feeding method and apparatus for a continuous plating apparatus for continuously feeding electric power to articles to be plated.
2. Description of the Related Art
Conventionally, in order to plate planar articles, a plurality of articles to be plated are individually mounted by fasteners on a frame member connected to cathodes, and the articles are removed individually after the completion of plating. However, this method is time-consuming, and causes a hindrance against plating work.
Therefore, recently, an approach has been proposed in which, without fixing the articles to the frame member, the articles to be plated are continuously fed into a plating bath one by one, and the articles to be plated are moved in a vertical direction within the plating bath to thereby continuously effectively plate the articles.
FIG. 7 is a cross-sectional view showing an example of a continuous plating apparatus that may perform continuous plating. A V-shaped rail 2 in cross section extending in a vertical direction to the paper surface is provided in the vicinity of a central bottom of a plating bath 1. An article 3 to be plated such as a printed circuit board is held in the vertical direction with its lower edge being laid on the rail 2. Both surfaces of the article 3 are clamped by electric supply rollers 5 fixed to vertical rotary electrode shafts 4. The electric supply rollers 5 are rotated together with the rotary shafts 4 so that the article 3 to be plated is moved horizontally on and along the rail 2 under the condition that the article 3 is dipped in plating liquid 6. Then, anodes 8 which may move vertically by cylinders 7 and shielding plates 9 for preventing turbulence are provided in the plating liquid 6.
Wheels 10 are mounted at suitable positions of the rotary shafts 4 and pressing members 12 pressed by springs 11 are brought into contact with the wheels 10. The pressure force of the springs 11 is transmitted from the wheels 10 through the rotary electrode shafts 4 to the electric supply rollers 5 so that the contact between the electric supply rollers 5 and the article 3 to be plated is ensured and the flow of the electricity to the surfaces of the article 3 is made uniform.
Thus, the surfaces of the article 3 to be plated are charged with a negative potential from the rotary electrode shafts 4 through the electric supply rollers 5 so that the current flows from the anodes 8 to perform the continuous plating.
The circumferential surfaces of the electric supply rollers 5 which are brought into contact with the articles 3 to be plated are coated with a protection film which is made of titanium nitride on, for example, a nickel plated film that is harder than the plating coating to be applied, such as a copper film. Brushes 14 are pressed against the circumferential surfaces of the electric supply rollers 5 by springs 13 so that the plating formed on the circumferential surfaces of the electric supply rollers 5 may be removed.
Since each of the conventional electric supply rollers 5 as a whole is formed into a single conductive member, the current always flows also through a portion which is out of contact with the article 3 to be plated and a plating is formed on the electric supply rollers 5 as a whole.
Even if the brushes 14 are depressed against the circumferential surfaces of the electric supply rollers 5 by the springs 13 as mentioned above, it is difficult to remove the plating adhered over the entire electric supply rollers 5. Due to the accumulated plating, the electric supply rollers 5 are damaged so that the serve life thereof is shortened. A current will not uniformly flow through the articles to be plated. As a result, it is impossible to perform the plating work.
According to the present invention, an electric feeding method of continuously electroplating a planar article comprising:
providing a plating apparatus having an anode, a cathode for flaking, and at least two rotary electrode shafts, each of said rotary electrode shafts having at least one electric supply roller mounted thereon;
dividing each of the electric supply roller in a circumferential direction into at least one conductive segment and at least one non-conductive segment;
clamping both sides of the planar article by the electric supply rollers such that the planar article is vertical;
moving the planar article horizontally through the plating apparatus by the rotation of the electric supply rollers;
electrically charging said at least one electric supply roller of said rotary electrode shafts so that the conductive segment in contact with the planar article has a negative potential; and
electrically charging said at least one electric supply roller of said rotary electrode shafts so that the conductive segment at a distance from the planar article has a positive potential, and an electric current flows between the cathode and the conductive segment which has the positive potential; is provided.
In the claimed method, the electric supply roller is divided into conductive and non-conductive segments and a planar article is plated by supplying a negative charge only to the conductive segment in contact with the planar article. The non-conductive segment and the conductive segment not in contact with the article of the same electric supply roller are prevented from undesirable plating. On the other hand, when the segment comes around to the opposite side of the electric supply roller by its rotation, a positive charge is supplied to the conductive segment. Thus, undesirable plating, which has adhered on the conductive segment charged negatively, elutes or flakes into a plating liquid so that the undesirable plating can be removed. Accordingly, the electric supply roller can be used for a longer term and the planar article can be uniformly plated by allowing a uniform electric current to flow to the planar article.
When the conductive segment of the electric supply roller rotates to the place at a distance from the planar article, an electric current flows between the conductive segment having a positive potential and the cathode, which pairs with the conductive segment. The cathode is provided in order to attract metal flakes, which are removed from the electric supply roller. The electric current flow is formed by supplying positive and negative charges from the same eliminator to the conductive segment and the cathode, respectively. The current flow results in drawing metallic flakes removed from the electric supply roller to the cathode, thus, the formation of a granulated surface by adhesion of the flakes on the plating face can be prevented.
Moreover, in the method of the present invention, a planar article is sandwiched between a pair of electric supply rollers so that the planar article is positioned vertically and conveyed by the pair. When a planar article has via holes, air inside them spontaneously flows out because of the rendering of the planar article vertical. Then, the insides of the via holes can be easily plated.
An electrical collection disk may be provided on an upper portion of each rotary electrode shaft, out of the plating liquid, in order to allow an electric current to flow to the electric supply roller. The electrical collection disk has conductive and nonconductive segments respectively corresponding to the conductive and non-conductive segments of the electric supply roller in phase in the circumferential direction. The electric supply roller and the electrical collection disk are fixed to the rotary electrode shaft in circumferential phase and are uniformly rotated by rotation of the shaft. Thereby, the electric supply roller can be efficiently charged via the rotary electrode shaft by contacting an electrode with the electrical collection disk.
The boundary between the conductive segment and the non-conductive segment is desirably formed to be vertical in the side face of the electric supply roller. In other words, it is desirable that each corner of the conductive segment is 90 degrees in the side face of the roller. If the corner of the conductive segment is an acute angle or the segment has a complex pattern in the side face, the undesirable plating thickens as the tip of the corner or the pattern narrows. Even if a positive charge is supplied to the conductive segment, a thick plating on the side face is likely to remain and all of the undesirable plating is hardly removed by supplying a positive charge. When the conductive segment, which has the remaining plating on the side face of the roller, rotates and contacts the planar article again, the undesirable plating causes flaws on the plating surface of the article. By forming the boundary between the conductive segment and the non-conductive segment to be vertical, if extra plating adheres near the boundary on the side face of the electric supply roller, the undesirable plating does not become so thick. Therefore, the undesirable plating can be efficiently removed by supplying a positive charge to the conductive segment.
When a positive charge is supplied for removing undesirable extra plating on the electric supply roller, pulsed current may be used. A large amount of pulsed current can flow at short-time intervals, although such a large amount of continuous current generates burst deposits on the electric supply roller. The pulsed current can efficiently flake the extra plating on the roller without forming burnt deposits, even if the undesirable plating is comparably thick. The pulsed current is desirably supplied at the rate of 9 A per 10 dm2 of the surface to be plated. On the other hand, in the case of continuous current, 3 A per 10 dm2 of the surface to be plated is preferable. The time-interval of the pulse is desirably set so that an integrated value of the pulsed current with respect to time is equal to a corresponding value of continuous current. For example, 1 ms of 9 A-current-carrying and 2 ms of keeping ground potential are alternately repeated as the pulsed current, in contrast with 3 A of current continuously flowing.
By the present invention, A continuous electroplating apparatus comprising:
a plating bath;
at least two rotary electrode shafts;
a rail between the rotary electrode shafts for mounting a planar article to be plated thereon;
an electric supply roller mounted on each of the rotary electrode shafts, the electric supply roller being divided into at least one conductive segment and at least one non-conductive segment;
an anode;
a cathode;
an electrical collection disk mounted on an upper portion of each of the rotary electrode shafts, the electrical collection disk corresponding to the electric supply roller mounted on the same rotary electrode shaft and having at least one conductive segment and at least one non-conductive segment in circumferential phase with the conductive segment and the non-conductive segment of the corresponding electric supply roller;
a first eliminator electrically connected to the conductive segment of the electric supply roller in contact with the planar article and to the anode; and
a second eliminator electrically connected to the cathode and to the conductive segment of the electric supply roller at a distance from the planar article is provided. The plating apparatus of the present invention continuously plates planar articles according to the claimed electric feeding method.
The continuous plating apparatus of the present invention has two eliminators. The first eliminator supplies a negative charge to the conductive segment of the electric supply roller in contact with a planar article to be plated and a positive charge to the anode in a plating liquid. Then, a flow of metal ions is formed in the plating liquid so that the metal ions produced at the anode are attracted to the planar article, thereby, the article is efficiently plated. On the other hand, the second eliminator provides a negative charge to the cathode in the plating liquid and a positive charge to the conductive segment at a distance from the planar article. Another flow of charges is formed in the plating liquid so that extra plating flaked off from the electric supply roller is attracted to the cathode. The electric charges supplied by the eliminators may be continuous current or pulsed.
A plurality of the electric supply rollers which respectively have one conductive segment may be provided to each rotary electrode shaft. Or, one electric supply roller having a plurality of the conductive segments may be provided to each rotary electrode shaft. In the case of the plural electric supply rollers mounted on each rotary electrode shaft, the electric supply rollers are displaced to each other in phase in the circumferential direction by an angle of the conductive segment. Thereby, a conductive segment of one of the electric supply rollers mounted on the same shaft always contacts with the planar article to be plated and keeps electrically charging without breaks. Furthermore, a plurality of electrically contacting points on the surface of the planar article are provided by distributing the plural electric supply rollers in an equal interval on the rotary electrode shaft. Thereby, the electric charge is uniformly spread on the surface of the planar article and a uniform plating face is formed on the surface.
The cathode of the claimed plating apparatus may be enclosed by a diaphragm. The diaphragm is made of a material which is impermeable to metal ions. Providing the diaphragm can prevent the metal flakes, which are removed from the electric supply roller, from adhering to the cathode. Accordingly, the cathode can be used for a long period of time without frequent replacements.